This project is a study of metabolic circadian rhythm in the heart. Such rhythms furnish unique opportunities to examine changing metabolic patterns that normally occur throughout the day. Circadian rhythms of myocardial glycogen, triglycerides and free fatty acids have been identified. Studies in progress are dealing with nutritional influences upon these rhythms, the relation of the myocardial rhythms to skeletal muscle rhythms and the mechanism that control these rhythms at the cellular level.